1. Technical Field
The present invention relates to a sheet feeding apparatus for separating and transporting sheets one at a time and an image forming apparatus equipped with this.
2. Related Art
In order to form a high-quality image on a recording sheet in an image forming apparatus which uses an electrophotographic method or an ink-jet method, an image forming process needs to be executed with appropriate parameters corresponding to the thickness, material, and so on of the recording sheet. For example, in order to suitably transfer a toner image formed on a photosensitive body to a recording sheet using an electrophotographic system, a transfer bias of the strength needs to be set corresponding to the thickness, material, and so on of the recording sheet. In an ink-jet system, the ink ejection patterns need to be changed in accordance with the thickness, material, and so on of the recording sheet.
Generally, recording sheets are placed in a sheet tray as a sheaf of plural stacked sheets, and sheets are separated one at a time from this sheaf of sheets and transported to an image forming portion. However, it sometimes happens that two sheets are transported at the same time due to the friction created between sheets (known as double-feeding). To prevent this kind of double feeding, a method is adopted in which a separating roller is provided to a position opposing a transporting roller, paper being separated one sheet at a time by rotating the separating roller in the same direction as the transporting roller.
In this case, the distance between the transporting roller and the separating roller needs to be adjusted in accordance with the thickness of the recording sheet. Further, to prevent skewing and jamming of the recording sheet, it is also effective to adjust the contact pressure when sandwiching the recording sheet between the transporting roller and the separating roller, in accordance with the thickness of the recording sheet. In order to perform these adjustments, the thickness of the recording sheet transported to the image forming portion needs to be measured ahead of the image forming process.